In Vitro Efficacy of Photodynamic Antimicrobial Chemotherapy with TONS504 Using Blue Light Against Pseudomonas aeruginosa

Background Pseudomonas aeruginosa is an important causative agent of bacterial keratitis. This study investigates the antibacterial effect of photodynamic antimicrobial chemotherapy (PACT) with the chlorin derivative TONS504 (TONS504-PACT) and a blue light-emitting diode (LED) on P. aeruginosa in vitro. It also explores the synergistic effects of combining TONS504-PACT with EDTA, and compares the antibacterial effects of TONS504-PACT using blue light with those of previously reported red light. Methods To evaluate the antibacterial effects of TONS504-PACT using blue light on P. aeruginosa, PACT with TONS504 (0-100 mg/L) was applied using a 405 nm LED at 0-30 J/cm2 to P. aeruginosa (107-8 CFU/mL). The antibacterial effects were assessed by calculating the survival fraction. Subsequently, to compare the effects of TONS504-PACT using blue light with those of using red light, PACT with TONS504 (10 or 100 mg/L) was conducted using a 405 or 660 nm LED at 30 J/cm2 and evaluated in the same manner. Finally, to investigate the synergistic antibacterial effects of TONS504-PACT with EDTA, PACT with TONS504 (0-100 mg/L) was applied using a 405 nm LED at 5 J/ cm2, both with and without EDTA (0.015 M), and its antibacterial effects were similarly assessed. Results TONS504-PACT using blue light decreased the survival of P. aeruginosa, depending on the light intensity. The greatest antibacterial effect was observed at 10 mg/L and 30 J/cm2, showing a survival fraction of 3.5 x 10-5. TONS504-PACT demonstrated a significantly greater antibacterial effect using blue light than that demonstrated using red light at 10 mg/L, though not at 100 mg/L. The combination of TONS504-PACT using blue light with EDTA significantly enhanced antibacterial effects at all concentrations. Conclusion These findings confirm the effectiveness of TONS504-PACT using blue light against P. aeruginosa and suggest its potential as a treatment for bacterial keratitis.